Apparently "off the grid" means something radically different to me
than it means to them, because here an "I'm off the grid"
vacation message would look more like

Hi. I'm currently out of the office for an off-the-grid vacation in
Lake Superior Provincial Park. If you have a really, truly urgent
matter that needs an immediate response from me, you are out of luck,
because there's not a chance in hell that I'm going to have any kind
of usable cellphone signal where I am. Knowing this, if you still need
to get a hold of me, you are going to have to come up with something
damn good -- good enough to convince the park rangers to tramp several
dozen kilometers through the wilderness after me and pull me out of the
bush. Good luck! Cheers, Rick

To be clear, I don't think that Kopelman or Feld are somehow wrong
or outlandish; I'm glad they have their autoresponder and it works for
them. They just live in a very, very different world from the one in
which I reside.